Vent silencers are used to silence high velocity air or gas flowing to and from the atmosphere, while also finding use in reducing discharge noises on air cylinders, vent lines, air motors, and the like.
One common form of vent silencer is the splitter type in which a perforated, rounded-nose bullet or splitter is mounted within the silencer housing and contains sound absorbing material. Sound energy passes through the holes or perforations and is absorbed in the material within the splitter.
A second common type of vent silencer is a tube-type in which a series of parallel perforated tubes are mounted within the housing and a sound absorbing material is packed around the tubes. The tube-type silencer acts to enhance the effectiveness of the sound absorbing material by providing an increased ratio of perimeter to flow passage cross sectional area. However, the tube-type of vent silencer has certain disadvantages. As the upstream ends of the tubes are normally open, high frequency sound energy can be beamed directly through the tubes. As a further consideration, erosion of the acoustic pack material surrounding the tubes can result due to direct impingement of the kinetic energy from the diffuser jets on the pack material. This problem has been particularly evident in vent silencer designs in which the primary diffuser extended radially or laterally with respect to the housing.
In an attempt to minimize this problem, radial diffusers in the past, have been constructed so that the portion of the diffuser facing the tube bundle has no holes or perforations.
The use of radial diffusers in a tube-type silencer has also generated aerodynamic noise due to the jets from the diffuser impinging upon the central plate which supports the upstream ends of the tubes. This aerodynamic noise was enhanced in prior designs by edge tone noise from the tubes themselves.